The Iowa AD--whoever it happens to be--is a paper tiger as long as KF remains the head coach.
KF's biggest, staunchest supporters are the program's biggest donors. Any AD "firing" BF without donor backing knows he or she would be run out of town on a rail. Because of that, no AD is ever going to fire BF without donor blessing.
There are lot's of things that could on paper technically happen, but never will. Your statement that an AD could fire Brian is less likely than pigs flying out of your ass.